Gears

Breakdown of the gear system:

Shifters: Shifters are the mechanism that allows you to change gears.  There are various types of Shifters.

Gripshifts. Mainly used on mountain bikes.

Downshifter. Used on some road bikes. Used on road/racing bikes.

Rapid fire shifters.  Used on Hybrid/Mountain Bikes.

Front Mech:  The front mech is used to move the chain between the front chainrings, whether there be two or three.

Rear Mech:  The rear mech is used to move the chain between the rear 'sprockets' on a cassette. 

Rear 'hub' gear.  A hub gear is an enclosed system of gears used on hybrid/commuter and some Mountain Bikes.  The advantage is that they are fairly maintenance free but tend to be heavier than cassette type gears.

Cassette:  A cassette is a group or block of sprockets of increasing sizes, varying in number from 5 through to 10 on higher specification road bikes. 

Single speed.  This type of system relies on only one cog on the rear wheel.  These bikes are low maintenenace but only have one gear.

Chain:  The chain is used to drive the bike forward by running over the chainrings and a sprocket.

The chain and gears wear out very easily if not maintained correctly.  One of the most important things to do is to make sure your drivetrain is clean and well lubricated.